This is a two-arm randomized controlled trial (RCT) for 308 seriously mentally ill adults (SMI) engaging in risky sexual and/or drug use behavior comparing a brief HIV primary and secondary prevention intervention [Skills building and Motivational Interviewing (SB-MI) to Care as Usual (CAU)]. Outcomes will be measured at 3, 6, and 12 months. The SB-MI intervention (3 sessions + booster) was initially developed as the experimental condition in an R34 pilot project which demonstrated its feasibility and promise. For the proposed project, we will recruit a larger sample which includes men and women, with and without HIV, from various ethnic and racial groups, different sexual orientations and housing arrangements, a range of psychiatric disorders and functional capacities. In this way we can more rigorously demonstrate the promise of SB-MI for diverse people with SMI. We will also conduct a sub-study after the 6 month follow-up to examine the impact at 12 months of an additional booster session for SB-MI participants. Our primary aim is to examine the effectiveness of a brief, tailored primary and secondary risk reduction strategy to CAU for people with serious mental illness. The desired outcomes for this aim include: decreased frequency of risk behaviors (number of partners, number of encounters); increased use of barrier precautions and IV needle cleaning; positive changes in information, motivation, and risk behaviors associated with HIV and increased HIV Counseling and Testing for those who do not know their HIV status. A second aim is to examine the effectiveness of a 2nd booster session after the 6 month follow-up for 1/2 of participants randomized to SB-MI. The primary outcome will be decreased frequency of risk behaviors and increased use of barrier precautions at the 12 month follow-up for participants who receive a 2nd booster. Our hypotheses include: 1) Effect sizes for constructs of the IMB (Information, Motivation, Behavior) Model will be larger for participants randomized to the SB-MI condition compared to CAU. 2) Participants in SB-MI will demonstrate higher rates of accessing HIV counseling and testing at follow-up, as compared to participants in CAU. 3) SB-MI participants who receive a 2nd booster session will be significantly more likely to maintain behavior change at 12 months compared to SB-MI participants who do not receive the 2nd booster. Our long-term objective is to reduce the incidence of HIV risk behavior for SMI using a brief intervention which can be easily translated and adapted to real world settings.